AU674868B2 - Improved shock tube structures - Google Patents

Description

AUSTRALIA

Patents Act COMPLETE SPECIFICATION

(ORIGINAL)

Class Int. Class Application Number: Lodged: Complete Specification Lodged: Accepted: Published: Priority Related Art: 9

S-

Name of Applicant: ICI Canada Inc.

S Actual Inventor(s): Robert Chauncey Greenhorn S* David John Welburn Address for Service: PHILLIPS ORMONDE FITZPATRICK Patent and Trade Mark Attorneys 367 Collins Street Melbourne 3000 AUSTRALIA Invention Title: IMPROVED SHOCK TUBE STRUCTURES Our Ref 340670 POF Code: 1453/1109 The following statement is a full description of this invention, including the best method of performing it known to applicant(s): -1- IMPROVED SHOCK TUBE STRUCTURES

BACKGROUND

The present invention is directed to improved shock tube structures for use as initiators for explosive events.

The field of initiators has become an intense field for invention over the past couple of decades. In an art that dates to the very beginning of civilization, change has been slow to come.

Past explosive events have typically been initiated by electric or 0 mechanical means through the use of electric or fuse cords, respectively, to connect the initial energy charge to the greater explosive charge.

*OS

In more recent times, a nonelectric nonfuse initiator has been used to begin the explosive event. A first leap in this field was recognized by Persson in U.S. Patent 3,590,739. There, a hollow plastic tube coated with a layer of explosive charge within the interior of the tube was found to effectively initiate the primary explosive. This tube is known as a shock tube in the explosive art. Generally, one end of the shock tube is ignited by a small explosion, as from a blasting cap, the ignition of reactive material within the shock tube thereby creates a F .ock wave which travels the length of the shock tube, and transfcLc the energy of the shock wave to an explosive charge at the other end of the shock tube.

As with any infant technology, the inventiveness of the initial nonelectric initiator shock tube was subject to the vagaries often associated with the first step in a new technology.

Improvements were made to solve certain continuity problems known to those skilled in this art, however, problems remained in actual field use. Typical of the problems encountered are impact k susceptibility, thermal cracking, and environmental ingresses, such as from organic solvents and/or water which may result in the failure of shock tube performance.

Inherent to the practice of the explosive art is the use of products in severe environments. As a consequence, explosive products must be able to withstand common usage in environments uncommon to most products. Temperatures may range from arctic to tropical extremes. The environmental conditions of the product may be solvent drenched in water, organic solvent, and/or some combination thereof or therebetween. Impact events may occur from any variety of solids smashing the shock tube product. As each environmental hazard is suffered, shock tube reliability and efficiency is risked. Since ready detection of bruised or damaged product is difficult to determine at times, product resilience 15" disclosed in Canadian Patent 1,200,718 issued February 18, 1986 to Simon et al, incorporated herein by reference. This particular embodiment discloses a sandwich type construction with a single plastic tube overcoated with a different and second plastic sleeve.

The present invention is found useful as a shock tube initiator and is found to be more resilient than prior constructions in the above stated environmental conditions. The resulting product is a layered construction as is disclosed hereinbelow.

A shock tube structure comprising a tube cons i ng of an exterior and an interior wall, said tube compri of EXEL shock tube material (Trademark of and obtained om the ICI Explosives business group, a part of which is Explosives US A Inc. and ICI Canada Inc. hereinafteri SURLYN shock tube material (Trademark of Du Pont may be obtained from ICI or the Ensign- Bickford Compan a shock tube) or some polyethylene, wherein Ssaid tubetion ir walls are coated by and communicate thereby with a re ive material and said tube exterior walls communicate with 0t9t -T i I~r ir 4 1iy nr -irnlyi2 SUMMARY OF INVENTION According to one aspect of the present invention there is provided a shock tube structure comprising a tube consisting of an exterior and an interior wall, said tube selected from the group consisting of polyethylene, poly(ethylene-comethacrylic acid) or polyethylene materials and blends thereof wherein said tube interior wall communicates with a reactive material, wherein said tube exterior wall communicates with a first outer layer said first outer layer comprises polymer alloys comprising a blend of two or more polymers at least two of which are selected from different classes of polymers being selected from the group consisting of polyamides, polyesters, polyurethanes and polyolefins, provided that said polymer alloy does not comprise a blend of a polyamide and a polyurethane, i said first outer layer optionally in communication with a second outer layer, said second outer layer consisting of the group selected from nylon, polyethylene, polymer alloy, thermoplastic, elastomer, combinations thereof and/or 15 therebetween, and, optionally, a first tie layer communicating with said exterior oo" wall and said first outer layer and, optionally, a second tie layer communicating with said first outer layer and said second outer layer.

According to a further preferred aspect of the present invention there is provided a shock tube structure comprising a tube consisting of an exterior and 20 an interior wall, said tube comprised of poly(ethylene-co-methacrylic acid) eg.

EXEL shock tube material (Trademark of an obtained from the ICI Explosives business group, a part of which is ICI Expolisves USA Inc. and ICI Canada Inc.

hereinafter SURLYN shock tube material (Trademark of Du Pont and may be obtained from ICI or the Ensign Bickford Company as a shock tube) or some polyethylene, wherein said tube interior walls are coated by an communicate thereby with a reactive material and said tube exterior walls communicate with a first outer layer said first outer layer comprised of a polymer 1, Ic EMY ORDVL.OAWORMSPA4829

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2a n POIYIfe.-V «Ulcy-( c.v.-cwprti5r NM~1c cund pOl-leii, g '.YTGL alloy, p~EL olymer alloy (Trademark of Du Pont and obtained from Du Pont, ZYTEL is a mixture of Nylon 6 and polyolefins, of particular preference is ZYTEL FE7101 as obtained from Du Pont) and/or blends thereof, wherein said first outer layer, optionally in communication with a second outer layer, optionally, a first tie layer communicating with said exterior wall and said first outer layer and, optionally, a second tie layer communicating with said first outer layer and said second outer layer. The tube is preferably made of either EXEL shock tube material, SURLYN 8940 or *i*0 SURLYN 8941 material, most preferably the tube is EXEL shock tube *e material.

The tube dimension is preferably 0.095 inches outside diameter with a 0.044 inches inside diameter The reactive or explosive material in the EXEL tube may be comprised of pentaerythritol tetranitrate ("PETN") cyclotetramethylenetetranitramine or powdered metal mixtures thereof such as aluminum. The coreload, the amount of reactive material coating the inside of the tube, ranges from about S" 7 milligrams per meter to about 30 milligrams per meter. A 9 q preferred coreload for the EXEL shock tube is about 16 milligrams per meter of HMX/A1 blend.

The outer first layer is comprised of a polymer alloy such as ZYTEL polymer alloy and/or blends thereof. Surprisingly, ZYTEL S polymer alloy is capable of intimate contact and/or communication with the EXEL shock tube. This is surprising since the EXEL shock tube is comprised of polyethylene derived materials and ZYTEL polymer alloy is comprised of nylon derived materials. Generally, nylons and polyethylenes do not make intimate interfacial contacts.

The blend mixtures of ZYTEL polymer alloy are, however, comprised of polyethylene and blends of polyethylene which may help to explain the above capability. Favored polyethylenes are linear low \density polyethylene (LLDPE) and medium density polyethylenes

(MDPE).

3 When the optional second layer is not present in the layered shock tube structure it is preferred that the outer first layer is comprised of the ZYTEL polymer alloy and blends thereof and most preferred that the outer first layer is the ZYTEL polymer alloy.

Polymer alloys are comprised of various individual polymeric homologues combined in a single phase when examined under electronmicroscopic methods, whereas at the same resolution, a polymer blend reveals multiphase morphology. Polymers used as blends and/or alloys may have molecular weights ranging from about 50 mass units up to about 150,000 mass units per repeating unit.

Mass units are typically taken as an average number of the polymers and/or copolymers which may be present. It is found that the outer first layer may continuously coat the tube providing an outside diameter for the tube/outer layer construction of up to about 0.118 inches.

The ZYTEL polymer alloy provides an outer first layer which is capable of exhibiting resilience in the harsh environments in which shock tubes may be forced to perform. However, it is found that Sthis outer first layer provides an excellent substrate for an optional outer second layer. When an outer second layer is present, the outer first layer may be comprised of other materials in addition to polymer alloys. In the multilayered construction, the properties sought for a resilient shock tube may be shared by the combined layers and provided by a multiple material construction. It is contemplated that more than two separate outer layers may be beneficially employed in a shock tube construction.

When the shock tube structure of the present invention is provided as a multilayered construction, the first outer layer is comprised of polymer alloy such as the ZYTEL polymer alloy, polyvinylenedichloride ("Saran"), polyethylene vinyl chloride polyvinylchloride any thermoplastic material, combinations of thermoplastic materials such as polyethersulfones and polyetherethersulfones rubber or elastomers, nylon 6 or nylon 66 such as MARANYL (trademark of and supplied by 4 ICI PLC), Kodar-PETG as blends from 5 to 95 weight percent (Kodar a trademark of and supplied by KODAK, Kodar PETG is generically known as ethylene-1,4-cyclohexylenedimethylene terephthalate, which is part of the family of thermoplastic polyesters of the PET [poly(ethylene terephthalates)]), Kodar and 5 to 95 weight percent blends of LLDPE, Kodar and 5 to 95 weight percent blends of Pellethane such as Pellethane 2103 and 2355 (from Dow Chemical), and polyesters such as RYNITE PBT (from Du Pont, of particular preference is Rynite RE6129) and 5 to 95 weight percent blends of MDPE. These materials are advantageously coated on said tube in thicknesses of up to about 0.118 inches for tube/outer first layer construction.

The outer second layer may also be comprised of the same material as the outer first layer when multilayers are combined.

It is preferred that the outer second layer is a dissimilar material to the outer first layer to enable the summation or cumulative effect of the different properties from each separate material employed. Examples of preferred outer second layers are SURLYN materials such as SURLYN 8940 and 8941, LLDPE, or MDPE and/or combinations thereof. It is most preferred that the outer second layer is comprised of either LLDPE or MDPE. At a minimum, the range of outer second layer thickness should be from, at a minimum, a continuous layer in communication with the outer first layer up to a maximum thickness of practical economic benefit. In composite, the tube/outer first layer/outer second layer outside diameter is preferably about 0.150 inches in OD. The most preferred construction is a tube with an inside diameter of about 0.044 inches and OD of about 0.095 inches, a tube/outer first layer construction OD of about 0.118 inches and a tube/outer first layer/outer second layer construction OD of about 0.150 inches.

Additional outer layers may be added of about up to 0.030 inches thickness.

Optionally, additional advantage is achieved with the introduction of a first and optionally a second or more tie layers between each, either, or some of the successive outer layers.

Examples of such tie layers are PLEXAR (trademark of and obtained from Quantum Chemical Corp.), BYNEL (trademark of and obtained from Du Pont), ADMER (trademark of and obtained from Mitsui Petrochemical Industries), and MODIC (trademark of and obtained from Mitsubishi Petrochemical Co., LTD). Tie layers are believed to promote adhesion and/or cohesion through activating the interfacial surfaces of the two disparate materials. Such tie layers may prevent wicking and/or interlayer creeping. Heat annealing, plasma corona discharging, flame, mechanical and/or chemical treatment of the layered constructions have a similar effect.

A further option is the addition of up to 5% of coupling agents, the coupling agents comprising the tie layer or some part thereof, such as KEN-REACT CAPS L12/L (Kenrich) and CRODAMIDE EBS (Croda Corp.) in each or all of the layers. Such compounds aid in dispersing nonmisable polymers in each other, provide inter-layer adhesion, ease flow of polymers and blends through extrur ion equipment and lower energy requirements.

Methods of manufacturing the layered shock tube construction are those which are generally known to those skilled in the art of tube/layered tube construction. Generally, the tube is vertically extruded, heating and extruding simultaneously. The interior portion of the tube is coated with a reactive material as the tube is formed, the tube is cooled then cold stretched. The tube may be annealed then overcoated with the outer first layer such as ZYTEL polymer alloy. The outer first layer may be added contemporaneous to the tube or added thereafter. The outer second layer and additional layers thereafter may be added by extrusion overcoating techniques known to those skilled in this art. In particular, it is preferred to overcoat the outer second layer off-line in a separate addition step.

Throughout the description and claims of this specification, the word "comprise" and variations of the word, such as "comprising" and "comprises", is not intended to exclude other additives, components, integers or steps.

Figure 1 is a transverse cross-section showing the tube and layers which comprise the layered shock tube; and Figure 2 is a cut away showing the continuous tube and layers which comprise the layered shock tube.

DETAILED DESCRIPTION Figure 1 shows a cross-section of a layered shock tube construction; the tube (1) has an inner wall and an outer wall In communication with the outer wall is the first outer layer Optionally, the second outer layer is in communication with the first outer layer In a further optional embodiment, a first tie layer interfaces with the outer wall and the inner wall and an optional second tie layer interfaces with the first outer layer and the second outer layer. Reactive material is coated on the inner wall to complete the operable construction of the layered shock tube.

Figure 2 shows a cut away wherein the tube is exposed as a continuous tube, the first outer layer is exposed as a continuous first outer layer, and the second outer layer is exposed as a continuous second outer layer.

•The Table shows the result of tests on layered shock tube having the above o described construction.

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0 0 0 a t s 0 a. @0 a a Ex. Layer Material O.D. Test Temnp Press Result Layer 1 KODAR PETG 0.118", Oil 50 0 C Over 5 days-ran 2 overcoat out of sample____ 2 KODAR in tube 0.118", oil 50 0 C 23hrs to failure 1 replacing EAA Cracking at 75lb load 20 0 C Cracks Impact Failure -400C 55% failure 10"1 3 IODAR/EVA 633 0.118", oil 50 0 C 20 days to failure 2 50/50 overcoat) 751b load 20 0 C Cracks 4 KODAR/EVA 633 0.118", oil 500C 42hrs to failure 2 25/75 Impact Failure -40 0 C 100% failure S bs, 5"1 KODAR/ATTANE 4403 0.118", Oil 50 0 C 42 hrs to failure 2 25/75 ______Impact Failure -400C 40% failure 6 KODAR/SURLYN 8941 0.118"1 751b load 20 0 C Cracks 2 50/50 Impact Failure -40 0 C 100% failure 5"1 Oil 150 0 C 15 days to failure

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S 054 S S S OS S S S S S S S S S S 0.

W.~r. T.avAl Material 0-n. Test 0* Temp Result Layer Ex Laver Maera 0. 7 KODAR/EAA 1430 0.118"' Oil 50 0 C 48hrs to failure 2 Impact Failure -400C 100% failure 5"1 8 KODAR/AI4PACET PEMB 0.118"1 Oil 500C 5 days to failure 2 10562 50/50 Impact Failure -400C 80% failure 5" 9 KODAR/SCLAIR 0.118", Oil 500C 21 days 2 E618-11 MDPE 50/50 Impact Failure -40 0 C 60% failure 5lbs, 5"1 KODA?./LLDPE 0.118", Oil 50 0 C 48 hrs to failure 2 SCLAIR 92-A 50/50 Impact Failure -40 0 C 100% failure lbs, 5"1 11 KODAR/EVA 633 0.150" Oil 500C 23 days, no 3 50/50 failures SURLYN 8941 Impact Failure -400CW 0% failure 501" 12 PBT(RYNITE) /E 618 0.118"1 oil 50 0 C 23 days, no 2 50/50 failures Impact Failure -20 0 C 100% failure 5"1 eec C. C

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C C C C C S 0* CS S Co C C C S C S CC CC C C S eec g C C CC 0 1~ i I Ex. Layer- Material 0. D. Test Temp Press Result Layer 13 DuPont ZYTEL 0.118", oil 50 0 C 21 days, no 2 failures Impact Failure -400C 0% failure 50"1 Water 2000 100 12 days, no failures 14 KODAR/4403 0.118", Gil 500C 9 days, no 2 50/50 Ifailures Impact Failure -200C 100t failure lbs, 5"1 KODAR/PELLETHANE 0.1181, Oil 5000 No failure 23 days 2 2103 50/50 _____Impact Failure -40 0 C Shatter 5lbs, 5"1 16 KODAR/LLDPE 124-C 0.11811 Impact Failure 400C, Shatters 2 50/50 17 KODAR/E 618 0.150"1 oil 5000 +23 days 3 50/50 STJRLYN 8941 impact Failure 400C 0% failure 50 18 Flexthaie 0.1001, oil 500C 2hrs; to failure 2

EXAMPLE

The Examples in the Table are presented to better understand the invention disclosed hereunder and are not intended to limit the scope thereof. All Examples were made by extrusion of an EXEL subtube, as per European patent application 89300462.2, filed January 18, 1989 by Greenhorn et al, herein incorporated by reference, followed by over-sleeving of the second and third layers. Over-sleeving means that an additional layer of material is applied to the substrate or subtube.

5. The samples were subjected to an oil test to simulate a common environmental 'hazard for shock tubing. The oil test involves submerging a mid-portion of a 2 meter long sample of the multilayer tubing, heat sealed at each end, in Shell Arctic grade diesel oil at 50 0 C. The heat sealed ends are kept out of the oil. From time to time, samples were "mnoved from the oil bath and initiated (exploded) from a dry end by conventional means (shot shell, primer, 1 spark gap initiator, detonator, etc). If the initiation produces a shock wave and the shock wave travels the length of the tube, *he tube is considered not to have failed.

A second environmental test devised to evaluate tube cracking at room temperature involved pressing a cross-over or doubli i te S tube on itself with 75 pounds (34 kg) of weight for approxima" ly seconds. The tube was Then visually inspected for cracks. A visible crack in the tube at the point of the test is considered a failure.

A third test involved the apparatus shown in Fig. 3. A 5 lb (2.27 kg) weight is allowed to drop from 5" (12.7 cm) to 50" (127 cm)in 5" increments onto 'the tube. The tube is held flat o. an Sanvil with the weight dropping thereon. After impact, the tube is initiated as 'in the first test. If the tube cracked and split sufficiently, the tube will fail to propagate a shock wave.

tube propagates past the impact point, it is considered to lbs and the height of the drop. This test can be done temperature or more generally at -40 0

C.

If the pass at at room A fourth test involved submerging jomplete dummy non-electric detonators in room temperature water at room temperature. The water was pressurized to 100 psi and samples removed and tested for propagation and ability to initiate a detonator.

*goo o* .k *goo 1 5 n D oa 00 *e 0 0S 00 a Result Table. Som EXAMPLE 1 EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 EXAMPLE 5 EXAMPLE 6 s of the tests of the various examples are given in the e comments related to specific examples follow: S Resulting tube was very stiff and cracked easily when bent.

S Some improvement, the tube exhibited surprisingly good powder adhesion properties but cracked fairly easily.

Tube was very stiff and prone to impact fracture.

Excellent oil resistance.

Stiff and not as efficient oil resistance.

Improvement in oil resistance, tube was stiff. 9 *a 0 Improvement in oil resistance, sensitive.

crack and impact EXAMPLE 7 EXAMPLE 8 \EXAMPLE 9 Impact sensitive and scme oil resistance.

Impact sensitive, good oil resistance but hard to process.

Excellent oil resistance, impact sensitive.

4 *e a aa EXAMPLE 10 EXAMPLE 11 EXAMPLE 12 EXAMPLE 13 EXAMPLE 14 EXAMPLE 15 EXAMPLE 16 EXAMPLE 17 EXAMPLE 18 Impact sensitive, poor oil resistance.

Excellent oil resistance, excellent impact performance, impact may cause deterioration of oil resistance.

Excellent oil resistance, impact sensitive but difficult to process.

Excellent performance in 3 tests as indicated.

Flexible even at -40 0 C. Versions made with blends and three layers also excellent.

Good oil resistance, impact sensitive.

Excellent oil resistance, but very impact sensitive.

Hard to run, very impact sensitive.

Stiff, excellent oil resistance and impact sensitivity.

Poor oil resistance, coating dissolved.

8S S a NOTE: (1)KODAR PETG is a trade nt .e of KODAK Chemicals.

SURLYN, ZYTEL and RYNITE are trade names of DuPont.

(2)Impact sensitive is defined as cracking easily when impacted.

Claims (18)

1. A shock tube structure comprising a tube consisting of an exterior and an interior wall, said tube selected from the group consisting of polyethylene, poly(ethylene-co-methacrylic acid) or polyethylene materials and blends thereof wherein said tube interior wail communicates with a reactive material, wherein said tube exterior wall communicates with a first outer layer said first outer layer comprises polymer alloys comprising a blend of two or more polymers at least two of which are selected from different classes of polymers being selected from the group consisting of polyamides, polyesters, polyurethanes and polyolefins, provided that said polymer alloy does not comprise a blend of a polyamide and a polyurethane, said first outer layer optionally in communication with a second outer layer, said second outer layer consisting of the group selected from nylon, polyethylene, polymer alloy, thermoplastic, elastomer, combinations thereof and/or therebetween, and, optionally, a first tie layer communicating with said exterior wall and said first outer layer and, optionally, a second tie layer communicating with said first outer layer and said second outer layer.

2. The structure of Claim 1 wherein said first outer layer comprises a polymer alloy comprising Nylon 6 and polyolefin. 20

3. The structure of Claim 1 or Claim 2 wherein said second outer layer is J-J- selected from the group consisting of poly(ethylene-co-methacrylic acid), linear low density polyethylene, medium density polyethylene, combinations thereof and/or therebetween.

4. The structure of Claim 1 or Claim 2 wherein said second outer layer is M 25 linear low density polypropylene or medium density polyethylene.

5. The structure of any one of Claims 1 to 4 wherein said first tie layer is g selected from the group consisting of maleic anhydride grafted polyolefins; low density polyethylene, linear low density polyethylene or polypropylene; polyolefin with grafted functional groups and graft ethylene-maleic anhydride copolymer, combinations therefor and/or therebetween.

6. The structure of any one of Claims 1 to 5 wherein said reactive material is selected from the group consisting of pentaerythritol tetranitrate, IM C WNVWORD\WLONAWORKPAS429 I DOC cyclotetramethylenetetranitramine, powdered metal mixtures thereof, combinations thereof and/or therebetween.

7. The structure of Claim 6 wherein said powdered metal is aluminium.

8. The structure of Claim 6 wherein said reactive material is a combination of cyclotetramethylenetetranitramine and aluminium powdered metal.

9. The structure of any one of Claims 1 to 8 wherein said polymer alloy comprises molecular weights from about 50 to 150,000 lass units per repeating unit.

10. The structure of any one of Claims 1 to 9 wherein said combined tube and first outer layer is about .118 inches in diameter.

11. A shock tube structure comprising a tube consisting of an exterior and an interior wall, said tube selected from the group consisting of polyethylene, poly(ethylene-co-metharcrylic acid) or polyethylene materials and blends thereof wherein said tube interior wall communicates with a reactive material, wherein said tube exterior wall communicates with a first outer layer said first outer layer is a polymer alloy selected from the group consisting of blends comprising a first tcomponent selected from the groups consisting of polyamides and terephthalate polyesters, and a second component selected from the group consisting of 20 polyolefins, polyurethanes, copolymers of ethylene and acrylic acid esters and oI" S copolymers of ethylene and metharcrylic acid esters, combinations thereof and/or therebetween, provided that said polymer alloy does not comprise a blend of f f polyamide and polyurethane, said first outer layer in communication with a second outer layer, said second outer layer selected from the group consisting of 25 nylon 6, nylon 66, polyvinylenechloride, polyethylene vinyl chloride, polyvinylchloride, linear low density polyethylene, medium density polyethylene, 0t polymer alloy, thermoplastic, elastomer, polyester, poly(ethylene-co-methacrylic acid), combinations thereof and/or therebetween, and optionally, a first tie layer communicating with said exterior wall and said first outer layer and, optionally, a second tie layer communicating with said first outer layer and said second outer layer. IM CWINWORDMLONA\WORKPAS42t. O:F 16

12. The structure of Claim 11 wherein said first outer layer is a polymer.alloy selected from the group consisting of:- blends comprising: Ethylene-1,4,cyclohexylenedimethylene terephthalate and low linear density polyethylene; blends comprising: Ethylene- 1,4-cyclohexylenedimethylene terephthalate and thermoplastic polyurethane elastomers; blends comprising: poly(ethylene terephthalate) and medium density polyethylene.

13. The structure of Claim 11 wherein said first outer layer is a mixture of Nylon 6 and polyolefns and said second outer layer is selected from the group consisting of linear low density polypropylene, medium density polypropylene, poly(ethylene-co-methacrylic acid), some combination thereof and/or therebetween.

14. The structure of Claim 1 wherein a couple agent comprises said first or second tie layers or a part thereof.

The structure of Claim 1 wherein said reactive material is provided as a coreload of about 16 milligrams per meter.

16. The structure of Claim 11 wherein said tub consists of an inside diameter of about 0.044 inches, an outside diameter of about 0.095 inches, a tube/outer layer first layer/outer second layer outside diameter of about 0.150 inches.

17. The structure of Claim 11 wherein said first outer layer is comprised' of a different material than said second outer layer.

18. A structure of Claim 1 or Claim 11 substantially as hereinbrfore described with reference to any one of the examples or drawings. L -DATED: 30 August 1996 S, ICI CANADA INC. t By their Patent Attorneys PHILLIPS ORMONDE FITZPATRICK i (1 ABSTRACT The present invention is directed to improved shock tubes wherein the improvement results in a shock tube more resilient to environmental loads placed on the shock tubes when in use. B 0 B e 0